1. Field of the Invention
The present invention relates generally to the orthotic field and, more particularly, to systems used by patients suffering a deficiency of the knee function due to injuries of the ligaments or connective tissues.
2. Description of the Related Art
Rupture or damage to the various knee ligaments causes episodes of knee instability and difficulties during walking, climbing stairs, etc. The damaged ligaments no longer provide the upper leg bone (femur) and lower leg bone (tibia) with the necessary restraints to keep them pivoting relative to each other in the normal manner.
For example, if the anterior ligament is damaged or ruptured, the knee loses the restraining force of the tibia during the extension movement from 60.degree. flexion into full extension. In this range of motion, the tibial bone frequently displaces forward (anteriorly), causes knee instability and loss of balance for the patient; consequently, the patient fails. Renstrom et al. have shown that the range of 60.degree. flexion-15.degree. extension causes an increasing strain in the anterior ligament. (See Renstrom, P., Arms, S., Stanwyck, T., et al., "Strain within the anterior cruciate ligament during hamstring and quadricep activity." Am. Journal Sports Medicine 14:83-87, 1986.) Hirokawa et al. have shown that indeed the tibial bone is displaced anteriorly in this range of motion and causes the strain in the ligament. (See Hirokawa, S., Solomonow, M., Lu, Y., et al., "Anterior-posterior and rotational displacement of the tibia elicited by quadriceps contraction." Am. Journal Sports Medicine 20:299-306, 1992.) Both Hirokawa et al. (See Hirokawa, S., Solomonow, M., Luo, Z., et al., "Muscular Co-Contraction and Control of Knee Stability." J. Electromyography and Kinesiology 1:199-208, 1991) and Renstrom et al. (above) have shown that mild to moderate contraction of the hamstrings can significantly reduce the anterior displacement of the tibia and the associated strain in the ligament which occurs in that range of motion.
The present applicants have shown that, during regular movement of subjects' intact healthy knees and elbows, mild to moderate contraction of the antagonist muscle (hamstrings during knee extension and triceps during elbow flexion) is the mode by which the nervous system maintains joint stability in daily movements. (See Solomonow, M., Baratta, R., Zhou, B., D'Ambrosia, R., "Electromyogram Coactivation Patterns of the Elbow Antagonist Muscles during Slow Isokinetic Movement." Experimental Neurology 100:470-477, 1988; Baratta, R., Solomonow, M., Zhou, B., et al., "Muscular coactivation: The role of the antagonist musculature in maintaining knee stability." Am. Journal Sports Medicine 16:113-122, 1988; Hagood, S., Solomonow, M., Baratta, R., et al., "The effect of joint velocity on the contribution of the antagonist musculature to knee stiffness and laxity." Am. Journal Sports Medicine 18:182-187, 1990.) Present applicants have also shown that such mild antagonist cocontraction could be increased in subjects and patients by training. (See Baratta, R., Solomonow, M., Zhou, B., et al., "Muscular coactivation: The role of the antagonist musculature in maintaining knee stability." Am. Journal Sports Medicine 16:113-122, 1988.)
Present applicants are also co-authors of other publications in this field, specifically as follows:
Solomonow, M., Baratta, R., Zhou, B., et al., "The synergistic action of the anterior cruciate ligament and thigh muscles in maintaining joint stability." Am. Journal Sports Medicine 15:207-213, 1987; PA1 Solomonow, M., Baratta, R., D'Ambrosia, R., "The Role of the Hamstrings in the Rehabilitation of the Anterior Cruciate Ligament-Deficient Knee in Athletes." Sports Medicine 7:42-48, 1989; PA1 Solomonow, M., D'Ambrosia, R., "Neural Reflex Arcs and Muscle Control of Knee Stability and Motion." Chapter 30, In: Ligament and Extensor Injuries of the Knee: Diagnosis and Treatment, ed. by W. N. Scott, C. V. Mossby, Hanover, Md., 1991; PA1 Solomonow, M., D'Ambrosia, R., "Neural Reflex Arcs and Muscle Control of Knee Stability and Motion." Chapter 6, In: The Knee, ed. by W. N. Scott, C. V. Mossby, Hanover, Md., 1994; and, PA1 Sanchez, J., Solomonow, M., Baratta, R., et al., "Control Strategies of the Elbow Antagonistic Muscle Pair During Two Types of Increasing Isometric Contractions." J. Electromyography and Kinesiology 3:33-40, 1993.
Co-applicant Solomonow is the inventor of the system disclosed in U.S. Pat. No. 4,781,180, entitled "Orthotic Knee Brace System and Method." The patent discloses an orthotic knee brace system which includes frameworks interconnected by a hinge and the use of a tibia stabilizing force transfer assembly that is operably interconnected between the frameworks. The force-transfer assembly includes means for gradually increasing the posteriorly directed retaining force at the upper anterior portion of the tibia as the leg extends, thereby preventing anterior dislocation of the tibia from the knee joint. In another embodiment, the force-transfer assembly includes means for gradually increasing the anteriorly directed retaining force at the upper posterior portion of the tibia as the leg begins flexion with the retaining force reaching a maximum as the leg reaches full flexion, thereby preventing posterior dislocation of the tibia from the knee joint.